Transcript Slide 1

INKLESS COLOR BLACKBOARD WITH MEMORY
COIL DESIGN
NANOMATERIAL
Department of Electrical &
Systems Engineering
Group 4
Lisa Fleming
Rafi Hasib
Easwaran Subbaraman
Advisors
Dr. Jorge Santiago
Dr. Dwight Jaggard
Special Thanks
Philip Farnum
Sid Deliwala
Sansern Somboonsong
Each display pixel requires its own magnetic field. By passing direct current
through loops of magnet wire, one can create an electromagnet to generate
such a field only when powered. Using the Law of Biot-Savart, one can
determine the field, B, at a particular distance from the loop of wire z, based
on its current I, radius r, and number of turns N.
This nanomaterial served as the inspiration behind the project. Given its ability to change color
when exposed to magnetic fields, it provides an ideal material to use for a multicolor display
with color resolution defined largely by the preciseness of magnetic field biasing points.
The material itself consists of "superparamagnetic
colloidal nanocrystal clusters" of iron oxide that form
"ordered structures when exposed to external magnetic
fields"
The diffraction wavelength (color) of the material can
altered by modulating the strength of the applied
field. A broad spectrum (red to violet) can be
varying the magnetic field strength from 50
500 gauss (violet), while the material
to any magnetic field is brown in
B
 Ir 2 N
0
2(r 2  z 2 )3 / 2
Furthermore, by use of a ferrite core within the loops of
wire, one can scale the field by a constant factor μrod, based
on the length-to-diameter ratio and the rod material’s
characteristics.
be
magnetic
created by
gauss (red) to
when not exposed
color.
The values for B, r, z, and I constrain the design to a
particular N but allow for freedom to choose wire diameter
d. A longer rod allows for a greater μrod but increases the
thickness of the board. Determining the right d presents a
tradeoff between pixel size and increase in resistance per
rod (and thus, power dissipation). All of these factors must
be considered in design.
ABSTRACT
Images of the nanomaterial when exposed increasing magnetic fields
The blackboard continues to remain a classroom
standard, allowing lecturers to visually communicate
information and erase it as necessary for reusability.
As society continues through the digital age, the
convenience of storing notes electronically has become
a more attractive means for preserving information.
Several products have been developed that attempt to
integrate these two ideas, often incorporating a
mounted projector with a computer to send and
receive information. However, the implicit
requirement of an overhead projector makes this a
very costly alternative to the traditional blackboard.
Furthermore, any extra embedded features offered, in
an effort to justify cost, detract from the primary
purpose of loading and storing written data.
In the chosen approach, a potentially cost-effective
alternative is explored, making use of electromagnets
within a self-contained device. Based on the
superparamagnetic, luminescent properties of an iron
oxide based nanomaterial, an array of electromagnetic
coils generates magnetic fields that alter the color of
the compound.
The hardware supporting each pixel is able to
accomplish two main goals: detecting when the stylus
has passed over a pixel, and then setting the current
through the electromagnet to produce the correct
magnetic field. A microcontroller, responsible for
activating the coils, also stores the state of the array
that can then be exported to an image file or
redisplayed on the board.
Stylus
Prototype coil
(3.5” length,
0.125” diameter,
31 AWG wire)
Save & Color Buttons
Pixel Hardware
(1) All quotes and images taken from:
Ge et al. “Self-Assembly and Field-Responsive Optical Diffractions of
Superparamagnetic Colloids”, American Chemical Society, 02/13/2008
Switch
Decoder
Electromagnet
Coil Array
Microcontroller
Differentiator
The hardware, which is identical for each pixel,
was designed to simultaneously detect when the
stylus passes over its respective pixel as well as to
keep the pixel’s electromagnet generating the field
needed to maintain color on the board.
System Startup
Image Formatter
Computer
Interface
Nanomaterial
Display
Once the pixel is detected as active, the coil’s color is set. The
two bits that the microcontroller outputs are the control bits
for a decoder. The decoder ensures that out of the four outputs
present (one for each color state), only one is active at a time.
Demo Times
Thursday, April 24, 2008
Pixel Hardware
Circuit Diagram
10:30 am – 12 noon
PIXEL HARDWARE
Process
Flowchart
Initialize memory
array for pixel
currents with zeros
Initialize all pixel
voltages to 0 V
Computer Display
When the stylus passes over the electromagnet, the
induced current in the coil creates a voltage spike
at the top of the coil with an amplitude of
approximately 30 mV. This node is the input to a
differentiator, which produces a voltage output
proportional to the change of the input voltage. This
voltage spike is amplified to register as a “high” input signal
to the microcontroller, as shown in the image on the right.
The proof-of-concept prototype that has been
developed allows the user to draw using one of three
colors, and erase as well. The size of the screen is three
pixels by five pixels so that single digit numbers and
most letters can be displayed.
2:00 pm – 3:00 pm
SYSTEM OVERVIEW
Illustration of the structure of iron
oxide colloids that have self
assembled when exposed to a
Optical microscope images showing magnetic field (1)
the assembly of CNC’s in a film
between two glass slides. The field
strength increases from (a to b) (1)
Wait for user action
Image of voltage spike:
differentiator output
To obtain different voltages for the
different colors, a voltage divider is used.
Each voltage is connected an analog
switch, all of whose ends are shorted
together. The control logic for the switches
is the decoder output, which ensures that
two different voltages will not be shorted
together. This voltage is connected to the
base node of a transistor, which isolates
the biasing voltages from the
electromagnet. The resulting current that
flows through the electromagnet produces
the correct magnetic field.
Change in Pixel
Current
Color Button Pressed
Change in Pixel
Current
Get ‘Color’
register value
Update ‘Color’
Register
Save Button
Pressed
The microcontroller serves as the central
processing core for the blackboard,
Allocate space in
Set pixel current
memory for array
coordinating detection of stylus swipes and
the corresponding setting of pixel color, saving
Update memory
Copy pixel array
the array state to memory, and clearing the
board when the user wishes to do so. The
microcontroller’s logic for these basic tasks is illustrated in the process flowchart above.
Detection of stylus swipes is interrupt-driven, thus minimizing microprocessor usage while
maximizing the response time to user input. Each interrupt updates the affected pixel’s color by
polling the color buttons and then outputting two bits to the decoder. These two bits represent
what color the pixel should be set to – three colors plus “erase”. The pixel hardware then sets the
coil voltage to the appropriate value. Finally the microcontroller updates its color value in the
array that stores the color values for all of the pixels in the
blackboard.
The save feature allows a user to save a copy of the blackboard’s
current state to the microprocessor’s memory. These saved
images can then be redisplayed by typing the save position into
the computer after specifying that a load is desired.
HC11 Microcontroller Board
MICROCONTROLLER & COMPUTER